The present invention relates to propellant casings including a substantially cylindrical casing body provided at one end thereof with a casing bottom and at another end thereof with a shoulder cone which terminates in a casing neck and which has an essentially uniform wall thickness. The present invention further relates to a method of making such propellant casings by drawing, from a steel blank, a preliminary cylindrical body with bottom, and subsequently shaping the casing bottom and the cylindrical casing body, and die-sinking the shoulder cone and the casing neck.
Propellant casings made of steel or weight-saving aluminum are well known. Reduction of ammunition weight has also been accomplished by producing steel propellant casings such that casing wall thicknesses are maintained at a minimum, particularly if the ammunition is to be transported by air.
For example, U.S. Pat. No. 2,915,424 discloses a method of making a propellant casing which involves the steps of coining a polygonal steel blank into a cup shaped piece, and subsequently deep drawing the piece through a series of successive annealing and drawing stages, after which the bottom and the neck of the casing are formed. Except for the regions adjacent the bottom of the casing, the cylindrical casing body, up to the front end of the casing neck, has a resulting wall thickness which is uniform.
Swiss Patent No. 503,966 discloses aluminum propellant casings that are produced from a cylindrical blank. The blank is reshaped into a cup-shaped piece before being deep-drawn. The casing bottom and the casing neck connected with the cylindrical casing body by the shoulder cone are shaped thereafter. The wall thickness is either uniform or decreases continuously from the casing bottom to the front region of the casing, and is enlarged in the region of the shoulder cone and the casing neck. The difference in thicknesses is due to the upsetting occurring during the formation of the cone and neck regions.
European Patent No. 0,096,186 discloses a steel propellant casing in which the wall thickness, which continuously decreases from the casing bottom toward the front of the casing, is increased in the region of the shoulder cone before the latter is formed. As a result, the wall thickness in the region of the shoulder cone will be uniform in the completed propellant casing. This measure seeks to avoid buckling in the region of the shoulder cone during loading of the cartridge into the weapon.
When conventional ammunition having steel propellant casings is fired, for example, from an automatic cannon having a rotary breechblock, as disclosed, for example, in U.S. Pat. No. 4,418,607, it has been found that frequent jamming of the breechblock and malfunctions during unloading of the weapon tend to occur.